A fuel injector is sometimes equipped with a nozzle positioned adjacent its outlet so that the fuel exiting the injector flows through a passage in the nozzle. Air can also be fed into the nozzle passage in addition to the fuel. The nozzle passage can be shaped and the pressure drop of the air through the nozzle can be controlled so that the air flowing through it achieves a sonic velocity resulting in the formation of a shock wave in the nozzle. The passage of the fuel through the shock wave increases the atomization of the fuel. This facilitates mixing of the fuel with the air prior to entering the cylinders of the engine and reduces the possibility of fuel condensing in the intake system after exiting the nozzle.
Numerous problems are associated with the use of such a nozzle. If the nozzle is not accurately aligned with respect to the fuel injector, the fuel exiting the injector can impinge on the walls of the nozzle passage. Contact between the fuel and the walls of the nozzle passage can result in fuel condensing in the nozzle passage making fuel atomization more difficult. In addition, impingement of the fuel on the walls of the nozzle passage can introduce turbulence resulting in a less predictable flow through the nozzle. Moreover, contact between the fuel and the walls of the nozzle passage can cause a reduction in the velocity of the fuel in the nozzle due to friction between the fuel and the nozzle thereby inhibiting fuel atomization, and mixing of the fuel and air.
Air can be provided to the nozzle through an air passage which feeds the nozzle through a single port. The port is typically formed in the wall of the nozzle so that the direction of the air flow into the nozzle is generally transverse to the direction of the fuel flow in the nozzle. The air stream entering the nozzle can direct the fuel toward the walls of the nozzle passage increasing the likelihood of fuel impingement on them. Moreover, the air passage leading to the port can have a perpendicular orientation with respect to the nozzle passage to further direct the air entering the nozzle passage squarely toward its wall opposite the port.
A further problem associated with such a nozzle is that the end from which the fuel exits is often blunt resulting in the fuel passing a generally flat surface upon exiting from the nozzle. Such a surface can be a prime site for fuel condensation.